Refrigeration & Air-Conditioning Practice Set-3

May 18, 2021

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1. Critical temperature is the temperature above which

A gas will immediately liquefy

A gas will never liquefy

Water will evaporate

Water will never evaporate

2. The C.O.P. of a refrigerator working on a reversed Carnot cycle is (where T₁ = Lowest absolute temperature, and T₂ = Highest absolute temperature)

(T₂ - T₁)/T₁

(T₁ - T₂)/T₁

T₂/ (T₂ - T₁)

T₁ / (T₂ - T₁)

3. The capillary tube, as an expansion device, is used in

All of these

Domestic refrigerators

Room air conditioners

Water coolers

4. The minimum temperature to which water can be cooled in a cooling tower is

Dry bulb temperature of air

Ambient air temperature

Dew point temperature of air

Wet bulb temperature of air

5. When the temperature of the surrounding is higher than the temperature of the body, then the heat loss by convection from the body to the surrounding will be

Negative

None of these

Positive

Zero

6. The freezing point of sulphur dioxide is

-75.2°C

-135.8°C

-77.7°C

-56.6°C

7. The value of C.O.P in vapour compression cycle is usually

Equal to unity

Any one of the above

Always more than unity

Always less than unity

8. In actual air-conditioning applications for R-12 and R-22, and operating at a condenser temperature of 40° C and an evaporator temperature of 5° C, the heat rejection factor is about

1.25

5.12

2.15

9. The condition of refrigerant after passing through the condenser in a vapour compression system is

Dry saturated vapour

Superheated vapour

Saturated liquid

Wet vapour

10. The refrigerant after condensation process is cooled below the saturation temperature before throttling. Such a process is called

None of these

Super-cooling

Normal cooling

Sub-cooling or under-cooling

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11. A human body feels comfortable when the heat produced by the metabolism of human body is equal to the

(B) Heat stored in the human body

(A) Heat dissipated to the surroundings

(D) Difference of (A) and (B)

12. The vapour compression refrigerator employs the following cycle

Carnot

Rankine

Reversed Rankine

Reversed Carnot

13. The bank of tubes at the back of domestic refrigerator is

Capillary tubes

Refrigerant cooling tubes

Condenser tubes

Evaporator tubes

14. Freon group of refrigerants are

Nontoxic and non-inflammable

Inflammable

Non-inflammable and toxic

Toxic

15. A bootstrap air cooling system has

One heat exchanger

Three heat exchangers

Four heat exchangers

Two heat exchangers

16. If a heat pump cycle operates between the condenser temperature of +27°C and evaporator temperature of -23°C, then the Carnot COP will be

0.2

1.2

17. A certain refrigerating system has a normal operating suction pressure of 10 kg/cm gauge and condensing pressure of about 67 kg/cm. The refrigerant used is

Brine

Freon

Ammonia

Carbon dioxide

18. Which of the following statement is correct?

(B) The increase in air movement increases the evaporation from the human body.

(D) Both (A) and (B)

(A) The human body can lose heat even if its temperature is less than the atmospheric temperature.

19. Mass flow ratio of NH₃ in comparison to Freon-12 for same refrigeration load and same temperature limits is of the order of

9: 1

1: 1

1: 3

1: 9

20. The general rule for rating refrigeration systems (excepting for CO₂ system) is to approximate following h.p. per ton of refrigeration

0.5 to 0.8 h.p. per ton of refrigeration

0.1 to 0.5 h.p. per ton of refrigeration

2 to 5 h.p. per ton of refrigeration

1 to 2 h.p. per ton of refrigeration

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21. The domestic refrigerator uses following type of compressor

Centrifugal

Piston type reciprocating

Axial

Miniature sealed unit

22. In a lithium bromide absorption refrigeration system

Lithium bromide is used as a refrigerant and water as an absorbent

None of these

Ammonia is used as a refrigerant and lithium bromide as an absorbent

Water is used as a refrigerant and lithium bromide as an absorbent

23. For obtaining high COP, the pressure range of compressor should be

Optimum

Low

High

Any value

24. Which of the following cycles uses air as the refrigerant?

Stirling

Bell Coleman

Carnot

Ericson

25. On the pressure-enthalpy diagram, condensation and desuperheating is represented by a horizontal line because the process

Involves no change in volume

Takes place at constant pressure

Takes place at constant temperature

Takes place at constant entropy

26. The boiling point of ammonia is

-10.5°C

-77.7°C

-30°C

-33.3°C

27. In a refrigeration system, the expansion device is connected between the

Condenser and receiver

Evaporator and compressor

Receiver and evaporator

Compressor and condenser

28. In a refrigeration system, heat absorbed in comparison to heat rejected is

Same

More for small capacity and less for high capacity

Less

29. The curved lines on a psychrometric chart indicates

Dry bulb temperature

Relative humidity

Wet bulb temperature

Dew point temperature

30. The atmospheric air at dry bulb temperature of 15°C enters a heating coil maintained at 40°C. The air leaves the heating coil at 25°C. The bypass factor of the heating coil is

0.6

0.4

0.67

0.376

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31. In a flooded evaporator refrigerator, an accumulator at suction of compressor is used to

Superheat the vapour

Collect vapours

Detect liquid in vapour

Collect liquid refrigerant and prevent it from going to compressor

32. Highest temperature encountered in refrigeration cycle should be

Much below critical temperature

Near critical temperature of refrigerant

Above critical temperature

At critical Temperature

33. Most thermostatic expansion valves are set for a superheat of

10°C

15°C

5°C

20°C

34. The change in evaporator temperature in a refrigeration cycle, as compared to change in condenser temperature, influences the value of C.O.P.

Unpredictable

Less

Equally

35. Which of the following is not a desirable property of a refrigerant?

High risibility with oil

Large latent heat

Low boiling point

Good electrical conductor

36. A thermostatic expansion valve in a refrigeration system

Ensures the evaporator completely filled with refrigerant of the load

None of the above

Is suitable only for constant load systems

Maintains different temperatures in evaporator in proportion to load

37. Rating of a domestic refrigerator is of the order of

5 tons

10 tons

40 tons

0.1 ton

38. A reversible engine has ideal thermal efficiency of 30%. When it is used as a refrigerating machine with all other conditions unchanged, the coefficient of performance will be

4.33

2.33

1.33

3.33

39. Cooling water is required for following equipment in ammonia absorption plant

Condenser, absorber and separator (rectifier)

Absorber

Condenser

Evaporator

40. The operating pressure for refrigerating units using R-12 as a refrigerant is

8 bar

15 bar

2 bar

30 bar

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A Demrot is the founder of VideRime Online Learning, a leading engineering website. He did his BE Civil and M.Tech Structure from RGPV University, Bhopal and has been working as an Assistant Professor in a reputed college.

Refrigeration & Air-Conditioning Practice Set-3

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